86 THE ENTOMOLOGIST. 



adopted by many collectors of attracting males by the exposure of a newly- 

 emerged female is usually productive of a series of the finest specimens. 



" I have myself observed in the case of Acidalia ruhricata, on a warm 

 evening in August, the extreme rapidity with which the males appear to 

 be developed, and how immediately they hurry to pay their attentions 

 to the scarcer and less active females which cling to the grasses and 

 occasionally rise to meet them in their flight. I can scarcely imagine 

 a colour better suited for rapid absorption of heat, with the exception of 

 black, than the beautiful dark red of fresh specimens of this insect, unless it 

 be perhaps the brilliant green of the under side of Thecla rubi. Applying 

 this to the more or less melanic varieties of high latitudes, I think we have 

 a sufficient explanation of the process of selection by which these varieties 

 are established and continued under the influence of a climate essentially 

 unfavourable to the paler forms. Those males whose colour enabled them 

 to absorb the heat most rapidly would naturally be the first to harden 

 their wings and to acquire a degree of vitality sufficient to enable them to 

 commence their flight. If we imagine the emergence of a pale and a dark 

 variety side by side at the same moment, it is more than probable that the 

 paler specimen would remain inactive among the herbage, when his darker 

 companion had already commenced his flight. In unfavourable weather 

 the degree of warmth sufficient to arouse even the darkest varieties might 

 be of very short duration, and if this were so the less favoured males 

 might be wholly deprived of the degree of energy necessary to enable them 

 to find their females. The shorter the continuance of passing gleams of 

 sunshine, the greater would be the influence brought to bear against them ; 

 and each separate instance, however uufrequent such instances might be, in 

 which they were thus placed at a disadvantage, would have its effect in 

 diminishing their numbers, promoting the survival of only the fittest forms. 

 If this is so it is sufficiently obvious that the first males on the wing have 

 the best chance of transmitting their colour by an hereditary process to the 

 succeeding generation ; and if these males were always or usually the 

 darkest of the brood, their progeny would also be for the most part dark." 



To ascertain whether it was a fact that a black or dark insect 

 would absorb more heat than a light-coloured one, the following 

 most interesting and conclusive experiments were made : — 



" To set this doubt at rest, I took advantage of the few sunny days 

 during the last fall of snow, with a view to test the comparative rapidity of 

 heat-absorption in some of our common Lepidoptera. On the 23rd of 

 January, at 11.30 a.m., I placed two specimens oi Tanagra cliarophyllata, 

 a black insect from the Yorkshire moorlands, and three of Acidalia im- 

 mutata, a white insect from the Norfolk fens, on a smooth surface of snow 

 exposed to bright sunshine at an angle of about 45°; with them I put a 



